Low-pressure electric discharge lamp, and electrode assembly therefor, having martensitic stainless steel anode



June 15, 1965 PERCENT OF CLEAN LAMPS F- W. HOEH LOW-PRESSURE ELECTRIC DISCHARGE LAMP, AND ELECT AS SEMBLY THEREFOR HAVING MARTENS I TI C STAINLESS STEEL ANODE Filed June 19, 1961 RODE FIG. I

Q so 3 MARTENSITIS STEEL r ANODES so i IN}, ANODES 40 o 2000 4000 e000 B000 10 000 BURNING-TIME IN HOURS MENTOR PRIOR TO DISCOLORATION FREDERICK 14 H056.

3,189,777 LOW-PRESSURE ELECTRIC DISCHARGE LAMP,

AND ELECTRODE ASSEMBLY THEREFOR, HAV- ING MARTENSITIC STAINLESS STEEL ANODE Frederick W. Hoeh, Livingston, N J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed June 19, 1961, Ser. No. 118,111 7 Claims. (Cl. 313-218) This invention relates to gaseous discharge lamps and, more particularly, to an improved fluorescent lamp.

One of the most serious and troublesome problems encountered in connection with electric discharge lamps, especially fluorescent lamps, is the progressive and pronounced decrease in light output which the lamp experiences during life. This problem has taken on added significance with the advent of highly-loaded fluorescent lamps having lighter fill gases and higher current densities than heretofore, One of the major factors contributing to this depreciation of light output during life is the an anode and electrode mount assembly wherein sputter- United. States Patent 3,189,777 Patented June 15, 19655 ice ' usual charge of mercury 17 and a filling of an inert ionizing of the anode and the resultant end blackening of the lamp are kept to a minimum.

The aforesaid objects, and others which will become apparent as the description proceeds, are achieved by fabricating the anodes from a preselected material that is more sputter-resistant than those used previously. More specifically, the anodes are fabricated from martensitic type stainless steel such as American Iron and Steel Institute (AISI) Nos. 440C or 420. Lamps having such anodes exhibit a marked improvement as regards end blackening compared to identical lamps having conventional anodes made from nickel or ferritic stainless steel.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGURE 1 is a side elevational view of a fluorescent lamp embodying this invention, a portion of the lamp being broken away for convenience of illustration;

FIG. 2 is an enlarged elevational view of one of the electrode mount assemblies employed in the lamp shown in FIG. 1;

FIG. 3 is a plan view of the mount assembly shown in FIG. 2; and

FIG. 4 is a graph comparing the mortality rates due to blackening of conventional fluorescent lamps and lamps embodying the present invention.

While this invention can be advantageously employed in various kinds of gaseous discharge lamps where sputtering and blackening are a problem, it is especially suited for use in fluorescent lamps and accordingly has been so illustrated and will be so described.

In FIG. 1 there is shown a fluorescent lamp 10 which generally comprises a tubular light-transmitting envelope 12 that is sealed at both ends and provided with suitable base members 13 and 14, such as recessed double-contact type bases of the character disclosed in US. Patent No. 2,983,838. Sealed into and extending axially inward from each end of the envelope 12 is a reentrant mount assembly 15 and 16, each of which carry the improved anodes 20 of this invention. The inner surface of the envelope is coated with a suitable UV-responsive phosphor 18 in the customary manner. The envelope also contains the able starting gas such as argon at about 2 mm. pressure. I

As shown more particularly in FIG. 2, the electrode mount assemblies each comprise a body member 22 of insulating material such as a glass flare one end whereof is press sealed around a pair of lead-in conductors 25 and 26. An exhaust tubulation 24 is fused to the stern press and communicates with an aperture therein. The inner lead sections protruding from the press are fabricated from relatively stilt wire such as nickel or thelike and are bent to form intermediate clamp portions 27 and Martensitic steel is a well-known special type of stainless steel that has been quenched during fabrication so as to have a surface hardness in the order of about 400 Brinell. Specific examples of such steels that have given excellent results are martensitic steel AISI No. 420, which has a hardness in the range of 495-555 Brinell, and A181 No. 440C, which has a hardness of about 550-600 Brinell.

As shown in FIGS. 2 and 3, the cathode is located be tween a pair of enlarged anodes 20 that are fastened as by spot welding to the lead wire arms 29. The anodes comprise rectangular plates of martensitic steel that are substantially coextensive with and extend along the sides of the cathode in parallel relationship therewith, as illustrated. In order to shield the lead wire arms 29 from the intense ionic bombardment in the region of the cathode they are preferably spot welded to the sides of the respective anodes opposite the cathode. With this construction sputtering of the leads and blackening from this source are reduced to a minimum.

While it is very difficult to verify in practice due to the many variables in lamp design, it is believed that the superior surface hardness of the martensitic stainless steel anodes 20 makes them more resistant to ionic bombardment and sputtering. However, whatever the reason, the use of such anodes has produced a marked reduction in the rate of blackening of lamps in which they are used. The order of improvement is shown in FIG. 4 wherein the dotted line curve 30 represents the mortality rate or the rate at which conventional lamps with nickel anodes developed objectionable degrees of blackening during life. As shown, all of the conventional lamps developed such blackening after only 800 hours of burning. In contrast, lamps of the same type equipped with the improved martensitic steel anodes of this invention showed no signs of blackening until after about 3000 hours burning, as indicated by the solid line curve 32. In other words, lamps having the improved anodes burned over 3 times longer without blackening than the best of the conventional lamps.

Moreover, as will be noted from the curve 32, even after 6000 hours of burning about 50% of the lamps having martensitic steel anodes remained free from discoloration, and roughly 6% of the lamps remained clean even after 10,000 hours.

Other comparative tests have shown that lamps having martensitic AISI No. 420 steel anodes exhibited no noticeable blackening after 5000 hours burning whereas only of the control lamps having ferritic No. 446 steel anodes remained clean after the same period of burning.

In view of the foregoing, it is apparent that the objects of the invention have been achieved in that a fluorescent lamp has been provided which can be economically and conveniently fabricated and which remains free from blackening for a much longer portion of its life than the prior art lamps. In addition, an anode and electrode mount assembly have also been provided which effects the aforesaid improvement with a minimum of parts and material.

While one embodiment has been described in detail, it is to be understood that various modifications in the configuration and arrangement of parts may be made Without departing from the spirit and scope of this invention.

I claim:

1. A low-pressure electric discharge lamp comprising, a light-transmitting envelope, spaced electrodes sealed within said envelope, and an anode of martensitic stainless steel located proximate each of said electrodes.

2. A fluorescent lamp comprising, a light-transmitting envelope having a phosphor coating on the inner surface thereof, a mount assembly sealed into each end of said envelope, each of said mount assemblies comprising a thermionic electrode and an enlarged anode of martensitic stainless steel held in spaced apart relationship by a body of insulating material.

3. A fluorescent lamp as set forth in claim 2 wherein said enlarged anode is fabricated from AISI No. 420 martensitic stainless steel.

4. A fluorescent lamp as set forth in claim 2 wherein said enlarged anode is fabricated from AISI No. 440C martensitic stainless steel.

5. .An electrode mount assembly for a fluorescent lamp or the like comprising, a vitreous body member, a pairof lead wires sealed throughand extending beyond said body member, an elongated cathode attached to and located between said lead wires, and an enlarged anode of martensitic stainless steel attached to one of said lead wires and supported thereby in a position adjacent said cathode.

d. An electrode mount assembly as set forth in claim 5 wherein said cathode comprises a refractory Wire coil coated with emission material, said enlarged anode of martensitic stainless steel comprises a rectangular plate that is substantially coextensive with and extends along the side of said cathode, and the lead wire supporting said enlarged anode is fastened to the face thereof opposite said cathode.

7. An electrode mount assembly as set forth in claim 5 wherein an elongated anode of martensitic stainless steel is attached to each of saidv lead wires and is supported thereby adjacent the respective sides of the cathode.

References (Iited by the Examiner UNITED STATES PATENTS 6/60 Kolkman 313-207 X 7/60 Morehead 3l3218 X 

5. AN ELETRODE MOUNT ASSEMBLY FOR A FLUORESCENT LAMP OR THE LIKE COMPRISING, A VITREOUS BODY MEMBER, A PAIR OF LEAD WIRES SEALED THROUGH AND EXTENDING BEYOND SAID BODY MEMBER, AN ELONGATED CATHODE ATTACHED TO AND LOCATED BETWEEN SAID LEAD WIRES, AND AN ENLARGED ANODE OF MARTENSITIC STAINLESS STEEL ATTACHED TO ONE OF SAID LEAD WIRES AND SUPPORTED THEREBY IN A POSITION ADJACENT SAID CATHODE. 